U.S. prosecutors cleared Chesapeake Energy Corp. and Encana Corp., two of the nation’s largest natural gas producers, of trying to cheat the state of Michigan in shale drilling auctions.

The Justice Department’s antitrust division sent a letter dated April 29 to Chesapeake saying the investigation has closed, according to a copy obtained by Bloomberg News. Encana confirmed in an emailed statement that it also had been informed the investigation was over. The department didn’t respond to voice mail messages seeking comment.

The wind-down of the federal grand jury inquiry is another step forward for Chesapeake out from under the shadow cast by former Chairman and CEO Aubrey McClendon, who was fired last year amid a shareholder revolt and conflict- of-interest scandal.

The decision to drop the case may bolster Chesapeake next week in a Michigan courthouse, where the state is pressing ahead with bid-rigging charges against both companies.

“More often than not, federal prosecutors and state attorneys general come to the same conclusion” because they are examining much of the same evidence, said Bruce McDonald, a partner at Jones Day and a former antitrust enforcer in the Justice Department.

As of the close of business Wednesday, the May 5 probable cause hearing into the state charges against Chesapeake and Encana was still scheduled to go forward, Sydney Allen, a spokeswoman for Michigan Attorney General Bill Schuette, said in a telephone interview.

During such a hearing, the accused can challenge whether the state attorney general had probable cause to bring the charges. Both companies pleaded not guilty in March.